Applicator Reconstruction in Gynecological Brachytherapy on MRI

Interstitial Brachytherapy and Applicators Libraries

Hospital Universitari Arnau de Vilanova (Lleida)

Summary (Actualizar)

  • Brachytherapy
  • Gynecological Brachytherapy
  • Imaging modalities: CT vs MRI
  • Applicator reconstruction
    • Applicators with interstitial part
  • Virtual planning

Brachytherapy

Brachytherapy vs External Beam Radiotherapy (Tele-therapy)

TrueBeam platform
Varian Medical Systems

MicroSelectron
Elekta

Brachytherapy modalities

High-Dose Rate (HDR)

Low-Dose Rate (LDR)

Pulsed-Dose Rate (PDR)

Brachytherapy modalities

High-Dose Rate (HDR)

Brachytherapy application

Cavum

Gynecological

Source Positions

Dose distribution

Differences between intracavitary and interstitial brachytherapy

Intracavitary brachytherapy

Interstitial brachytherapy

Brachytherapy workflow

Image adquisition

Contouring

Reconstruction

Dosimetry

Treatment delivery

Brachytherapy workflow

Reconstruction

Commons Locations

Prostate

Gynecological

Breast

Head and Neck

Ophthalmic

Commons Locations

Gynecological

Gynecological Brachytherapy HDR

Indications

Cervical Cancer

Endometrial Cancer

Vaginal Cancer

Indications

Cervical Cancer

MRI golden standart

MRI vs CT: Cervix

MRI vs CT: Applicator

Reconstruction in Brachytherapy

Problem Statement

  • The problem is a conversion from 3D to 1D due to the constraints involved.
  • Most distal position as origin of l parameter.

Impact on dose distribution

DVH parameters

  • Bladder and rectum in ant-pos direction: 5%-6% per mm
  • Rest of organs and directions: 4% per mm

Warning

Systematic errors of a few millimetres can lead to significant deviations (More than 10%).

Direct Reconstruction (DR)

The most distal stopping position (tip position) and the trajectory of the source on the image must be identified.

Pros

  • This is the most intuitive and straightforward way to do it.

Cons

  • Trajectory and/or tip position of the source may not be visible
  • Slice thickness

Dummies CT

Dummies MRI

Caution

There are no commercial dummies for MRI compatible needles.

Applicator Libraries (AP)

Limitations

When using several rigid applicators each applicator should be imported separately, since there is a risk that the position of the applicators in relation to each other could change inside the patient.

Focus on MRI-compatible applicators

Plastic applicators

Metallic applicators (titanium)

Imaging Modalities
CT vs MRI

The use of imaging in brachytherapy

CT-guided brachytherapy

Transition to MRI

Image registration

MRI-guided exclusive brachytherapy

Virtual
Planning

Presentation of the problem

The Benidorm applicator

Contributions

ALFIM2016

Characterization of a Gynaecological Titanium Applicator for Direct Reconstruction on MRI (AAPM2019)

Novel Semi-Automatic Reconstruction Method for Plastic Gynaecological Applicators (AAPM2019)

A novel tool for the reconstruction of the Utrecht applicator on MRI (ABS2021)